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RE: Subgrade Drag Equation

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Keep in mind that shrinkage is greater with a higher total cement(water) content in your concrete


If you specify low w/c you could get a mix with low w/c but very high cement content – more paste for workability – more shrinkage; don’t specify more strength than you need. Consider a larger aggregate size and limits on total cement content to obtain a concrete that has less shrinkage.


Is it true that shrinkage control reinforcement does not get mobilized until the concrete cracks? If they really want a large joint-less surface, would PT work? I imagine that a PT SOG would cost more than adding a few extra joints though.




From: Mark Puccio [mailto:mpuccio(--nospam--at)]
Sent: Monday, May 11, 2009 12:09 PM
To: seaint(--nospam--at)
Subject: Subgrade Drag Equation


We are working on an industrial farm project that has a large slab-on-ground. All joints need to have waterstop installed, so we have been told to minimize the number to as few as possible.  I was given, by our client, a reference for joint spacing using the subgrade drag equation.  This reference refers to ACI 360 of which I have the ACI360R-06 but do not find this equation in it.  It also shows joint spacing at 79-feet with #4 at 18. Wow this sounds like cracks waiting to happen.  Not wanting to get sued spurs some questions.


Does anyone know if this equation is acceptable with current ACI?

Has anyone used this type of spacing with good results?

Is this in the 360R-06 or where might if find it.

Besides good curing, low W/C ratio what other factors (besides shrinkage compensating concrete $) were used in your successful project?